Indium gallium zinc oxide

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Indium gallium zinc oxide (IGZO) is a semiconducting material, consisting of indium (In), gallium (Ga), zinc (Zn) and oxygen (O). IGZO thin-film transistors (TFT) are used in the TFT backplane of flat-panel displays (FPDs). IGZO-TFT was developed by Hideo Hosono's group at Tokyo Institute of Technology and Japan Science and Technology Agency (JST) in 2003 (crystalline IGZO-TFT) [1] [2] and in 2004 (amorphous IGZO-TFT). [3] IGZO-TFT has 20–50 times the electron mobility of amorphous silicon, which has often been used in liquid-crystal displays (LCDs) and e-papers. As a result, IGZO-TFT can improve the speed, resolution and size of flat-panel displays. It is currently used as the thin-film transistors for use in organic light-emitting diode (OLED) TV displays.

IGZO-TFT and its applications are patented by JST. [4] They have been licensed to Samsung Electronics [4] (in 2011) and Sharp [5] (in 2012).

In 2012, Sharp was the first to start production of LCD panels incorporating IGZO-TFT. [6] Sharp uses IGZO-TFT for smartphones, tablets, and 32" LCDs. In these, the aperture ratio of the LCD is improved by up to 20%. Power consumption is improved by LCD idling stop technology, which is possible due to the high mobility and low off current of IGZO-TFT. [7] Sharp has started to release high pixel-density panels for notebook applications. [8] IGZO-TFT is also employed in the 14" 3,200x1,800 LCD of an ultrabook PC supplied by Fujitsu, [9] also used in the Razer Blade 14" (Touchscreen Variant) Gaming Laptop and a 55" OLED TV supplied by LG Electronics. [10]

IGZO's advantage over zinc oxide is that it can be deposited as a uniform amorphous phase while retaining the high carrier mobility common to oxide semiconductors. [11] The transistors are slightly photo-sensitive, but the effect becomes significant only in the deep violet to ultra-violet (photon energy above 3 eV) range, offering the possibility of a fully transparent transistor.

The current impediment to large-scale IGZO manufacturing is the synthesis method. The most widely used technique for transparent conducting oxide (TCO) synthesis is pulsed laser deposition (PLD). [12] In PLD, a laser is used to focus on nano-sized spots on solid elemental targets. Laser pulse frequencies are varied between the targets in ratios to control the composition of the film. IGZO can be deposited onto substrates such as quartz, single-crystal silicon, or even plastic due to its ability for low-temperature deposition. The substrates are placed in a PLD vacuum chamber, which controls oxygen pressure in order to ensure favorable electrical properties. After synthesis, the film is annealed, or gradually exposed to air to adjust to the atmosphere.

While PLD is a useful and versatile synthesis technique, it requires expensive equipment and plenty of time for each sample to adjust to regular atmospheric conditions. This is not ideal for industrial manufacturing.

Solution processing is a more cost effective alternative. Specifically, combustion synthesis techniques can be used. Kim et al. used a metal nitrate solution with an oxidizer to create an exothermic reaction. [13] One common type of combustion synthesis is spin coating, [14] which involves depositing In and Ga solution layers onto a hot plate and annealing at temperatures roughly between 200 and 400 degrees C, depending on the target composition. The films can be annealed in air, which is a large advantage over PLD.

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A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directly but instead use a backlight or reflector to produce images in color or monochrome.

<span class="mw-page-title-main">Organic electronics</span> Field of materials science

Organic electronics is a field of materials science concerning the design, synthesis, characterization, and application of organic molecules or polymers that show desirable electronic properties such as conductivity. Unlike conventional inorganic conductors and semiconductors, organic electronic materials are constructed from organic (carbon-based) molecules or polymers using synthetic strategies developed in the context of organic chemistry and polymer chemistry.

<span class="mw-page-title-main">OLED</span> Diode that emits light from an organic compound

An organic light-emitting diode (OLED), also known as organic electroluminescentdiode, is a type of light-emitting diode (LED) in which the emissive electroluminescent layer is an organic compound film that emits light in response to an electric current. This organic layer is situated between two electrodes; typically, at least one of these electrodes is transparent. OLEDs are used to create digital displays in devices such as television screens, computer monitors, and portable systems such as smartphones and handheld game consoles. A major area of research is the development of white OLED devices for use in solid-state lighting applications.

A thin-film transistor (TFT) is a special type of field-effect transistor (FET) where the transistor is made by thin film deposition. TFTs are grown on a supporting substrate, such as glass. This differs from the conventional bulk metal oxide field effect transistor (MOSFET), where the semiconductor material typically is the substrate, such as a silicon wafer. The traditional application of TFTs is in TFT liquid-crystal displays.

<span class="mw-page-title-main">Flat-panel display</span> Electronic display technology

A flat-panel display (FPD) is an electronic display used to display visual content such as text or images. It is present in consumer, medical, transportation, and industrial equipment.

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A television set or television receiver is an electronic device for the purpose of viewing and hearing television broadcasts, or as a computer monitor. It combines a tuner, display, and loudspeakers. Introduced in the late 1920s in mechanical form, television sets became a popular consumer product after World War II in electronic form, using cathode ray tube (CRT) technology. The addition of color to broadcast television after 1953 further increased the popularity of television sets in the 1960s, and an outdoor antenna became a common feature of suburban homes. The ubiquitous television set became the display device for the first recorded media for consumer use in the 1970s, such as Betamax, VHS; these were later succeeded by DVD. It has been used as a display device since the first generation of home computers and dedicated video game consoles in the 1980s. By the early 2010s, flat-panel television incorporating liquid-crystal display (LCD) technology, especially LED-backlit LCD technology, largely replaced CRT and other display technologies. Modern flat panel TVs are typically capable of high-definition display and can also play content from a USB device. Starting in the late 2010s, most flat panel TVs began to offer 4K and 8K resolutions.

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<span class="mw-page-title-main">Organic field-effect transistor</span> Type of field-effect transistor

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<span class="mw-page-title-main">AMOLED</span> Display technology for use in mobile devices and televisions

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An oxide thin-film transistor or metal oxide thin film transistor is a type of thin film transistor where the semiconductor is a metal oxide compound. An oxide TFT is distinct from a metal oxide field effect transistor (MOSFET) where the word "oxide" refers to the insulating gate dielectric. In an oxide TFT, the word oxide refers to the semiconductor. Oxide TFTs have applications as amplifiers to deliver current to emitters in display backplanes.

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Douglas A. Keszler is a distinguished professor in the Department of Chemistry at Oregon State University, adjunct professor in the Physics Department at OSU and adjunct professor in the Department of Chemistry at University of Oregon. He is also the director of the Center for Sustainable Materials Chemistry, and a member of the Oregon Nanoscience and Microtechnologies Institute (ONAMI) leadership team.

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References

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